Effects of Line Dynamics on Stability Margin to Hopf Bifurcation in Grid-Forming Inverters

TL;DR

This paper analyzes how line dynamics influence the stability margin of grid-forming inverters near Hopf bifurcations, identifying key control parameters and showing line dynamics generally reduce stability margins.

Contribution

It provides an analytical sensitivity expression for stability margins and highlights the impact of line dynamics on inverter stability, especially on voltage-reactive power droop gain.

Findings

Feedforward gain in voltage control improves stability margin.

Line dynamics cause a uniform reduction in stability margin.

Reactive power droop gain is most affected by line dynamics.

Abstract

This paper studies the parameter sensitivity of grid-forming inverters to Hopf bifurcations to address oscillatory instability. An analytical expression for the sensitivity of the stability margin is derived based on the normal vector to the bifurcation hypersurface. We identify the most effective control parameters through comprehensive analysis. In particular, the impacts of line dynamics on the stability margin to Hopf bifurcation are investigated. The results indicate that the feedforward gain in the voltage control loop is the most effective parameter for enhancing the stability margin. Furthermore, it is observed that line dynamics introduce a uniform reduction in the stability margin across all parameters. However, the reduction is generally small for most parameters except for the voltage-reactive power droop gain, which shows a more pronounced effect.